Dynamic Alarm Conditions

As mentioned above in the section Configuration of a peripheral address, the node ID of the alarm condition must be configured in the address to map the alarm to a DPE. As there are situations in which this node ID cannot be determined in advance or only with difficulty, the fallback address option has been introduced - see below. This also makes it possible to receive alarms that have a dynamic condition ID. This is the case, for example, for the OPC UA server of a PLC 1500.

Configuration

In order to support also the reception of alarms without configuration of the ConditionId the concept of a fallback address is used. This allows that all alarms, which are received via an alarm subscription and which are not mapped to an explicit configured ConditionId are mapped to an arbitrary fallback alarm address.

This fallback address can be configured with the config entry [opcua] alarmFallbackAddress. In such a case the receiving DPE might have many active alarm instances, which is possible because the _alert_hdl used a multi-instance alarm.

If more than one condition is mapped to a DPE you should always select UA Alarm text and UA Severity in the subscription, because different conditions might have difference alarm text and severity.